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Enterprise JavaBeans, Second Edition by Richard Monson-Haefel

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Passing Objects by Value

Passing objects by valueis tricky with Enterprise JavaBeans. Two simple rules will keep you out of most problem areas: objects that are passed by value should be fine-grained dependent objects or wrappers used in bulk accessors, and dependent objects should be immutable.

Dependent Objects

Dependent objects are objects that only have meaning within the context of another business object. They typically represent fairly fine-grained business concepts, like an address, phone number, or order item. For example, an address has little meaning when it is not associated with a business object like Person or Organization. It depends on the context of the business object to give it meaning. Such an object can be thought of as a wrapper for related data. The fields that make up an address (street, city, state, and Zip) should be packaged together in a single object called Address. In turn, the Address object is usually an attribute or property of another business object; in EJB, we would typically see an Address or some other dependent object as a property of an entity bean.

Here’s a typical implementation of an Address:

public class Address implements java.io.Serializable { private String street; private String city; private String state; private String zip; public Address(String str, String cty, String st, String zp) { street = str; city = cty; state = st; zip = zp; } public String getStreet() {return street;} public String getCity() {return city;} public String getState() ...

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